Exemplary embodiments relate to a nonvolatile memory device including page buffers and a method of reading the same.
There is an increasing demand for nonvolatile memory devices that can be electrically programmed and erased and which do not require refreshing at specific intervals.
The nonvolatile memory device can be electrically programmed and erased in such a way that electrons within an oxide layer are moved by a strong electric field applied to the oxide layer, thereby shifting threshold voltages of memory cells.
In order to read data stored in the memory cells of the nonvolatile memory device, resetting is performed and the sense node of a page buffer is then precharged to a high level by precharging a bit line.
When the nonvolatile memory device is a multi-level cell (‘MLC) program method or a triple level cell (TLC’) program method, a read operation is performed twice or more on the basis of different reference voltages.
When the read operation is repeated, the read operation for some of the memory cells is completed according to threshold voltages of the memory cells. In a typical read method of the nonvolatile memory device, precharging is performed for all memory cells every time. That is, such precharging is performed for some of the memory cells that have already been read.
Accordingly, not only is the consumption of an operating current increased, but also a source line bouncing phenomenon occurs where a lot of current flows through a source line according to a cell string coupled to the bit line. Consequently, a problem arises because a threshold voltage distribution of the memory cells is widened.